Pressure relief valves are widely used in motor vehicles to relieve air pressure surges or peaks in the passenger compartment which result for example, when the doors are slammed shut. The valves generally comprise a simple rigid frame or housing which mounts in an aperture in a vehicle body panel. A valve element in the form of a normally flexible plastic flap is connected to the frame to overlie the aperture in the vehicle body panel. The valve element opens relative to the frame to uncover the aperture to relieve air pressure surges.
U.S. Pat. No. 5,715,782 discloses a composite molded butterfly valve for an internal combustion engine. A valve housing forms combustion air through passages and an axially extending valve bore defines an axis through the valve housing and bisects the through passages. Molded integrally within the valve housing is a molded composite valve member having an axial valve shaft, disposed in predetermined through bores. The valve member is rotatable in the valve bore to open and close the valve plates for regulation of air flow.
U.S. Pat. No. 4,546,695 discloses a grille unit for a vehicle with a frame and a vane pivotally connected to the frame via opposing first and second shafts. The frame has first and second holes snugly receiving the first and second shafts respectively. The first shaft has a peripheral surface, the diameter of which continuously varies along the axis thereof. The second shaft has a similar peripheral surface. The varying diameter surfaces of the first and second shafts face in opposite directions. The frame has a first inner surface which conforms to the varying diameter surface of the first shaft to engage the latter. The frame has a second inner surface which conforms to the varying diameter surface of the second shaft to engage the latter. A method of manufacturing the grille unit includes the steps of forming the frame from plastic, and assembling a mold with the frame positioned within the mold. A soft plastic is injected into the mold until the injected soft plastic fills the first and second holes of the frame.
U.S. Pat. No. 5,298,215 discloses a method for injection molding of objects of at least two independent parts, which are connected non-detachably but mutually rotatably, the subsequently produced part being injected at least partially into a mold recess of the previously produced part. An approximately hollow, cylindrical element is molded to the part produced first, in the region connecting this part to a rotatable part, that is to be produced subsequently. The hollow, cylindrical element is thereupon surrounded by a mold for the subsequent part and for the production of this part, either the outer space of the hollow cylindrical element which is closed off by a core, or the inner space of this hollow cylindrical element, which is not closed off, is injected for the production of this part. The part produced first is deformed in the region of the hollow cylinder into an undercut with rotational symmetry by the pressure of the material injected.
There exists a need for a pressure relief valve which consists of an integrally molded design with no subsequent assembly required before placement into the aperture in the body panel of the motor vehicle. There also exists a need for a pressure relief valve which has a low friction connection between the valve element and the frame so as to reduce an amount of torque required to open the valve element.